1. Field of the Invention
The present invention relates to a rotary type electrostatic spray painting device.
2. Description of the Related Art
In a painting operation line for painting bodies of motor vehicles, a method of painting the color determined for each body conveyed on the painting line is normally adopted. Consequently, where the color of the paint now used is different from the color to be painted next, it is necessary to clean the rotary type electrostatic spray painting device during the time elapsing between the completion of the painting operation of one vehicle body and the starting of the painting operation of the next vehicle body. At present, it takes a very long time to clean the painting device, and the conveyer speed of the painting line depends on such a cleaning time. Consequently, it is very important to shorten the cleaning time in order to increase the speed of the conveyer, and thereby increase productivity.
Where a clear paint or solid paint is sprayed by a rotary type electrostatic spray painting device, a good paint surface can be obtained by rotating the spray head of the painting device at about 15,000 r.p.m. However, where metallic paint is sprayed by the rotary type electrostatic spray painting device, if the rotating speed of the spray head is lower than 45,000 r.p.m. pieces of aluminium foil contained in the metallic paint can not be suitably aligned with each other, and a good finish can not be obtained. As a result, it is difficult to obtain a good paint surface.
The spray head of the painting device is normally rotated by means of an air turbine. When the color of the paint to be sprayed is to be changed, the air injecting operation by the turbine nozzles is stopped so that the rotating speed of the spray head decreases. Then the cleaning operation of the painting device is carried out. However, where the spray head is rotated at about 45,000 r.p.m., even if the air injecting operation by the turbine nozzles is stopped in order to change the color of the paint, about ten seconds must pass before the rotating speed of the spray head is reduced to 30,000 r.p.m. This causes a drawback in that, if a cleaning liquid, that is, thinner, is fed onto the spray head while the spray head is rotated at about 30,000 r.p.m, waste thinner containing paint therein is scattered, and this scattered waste thinner adheres to the housing of the painting device. Subsequently, when the operation of painting the following vehicle body is carried out, the waste thinner on the housing of the painting device is attracted towards the vehicle body to be painted, due to the electrostatic force, and adheres thereto, causing paint defects. Consequently, where the spray head is rotated at over 45,000 r.p.m. in order to spray metallic paint, when the supply of air from the turbine nozzles is stopped in order to change the color of the paint, it is necessary to wait for a long time until the rotating speed of the spray head is considerably reduced. This results in a problem in that the time for cleaning the spraying device becomes overlong.